Gas turbines are used in many sectors for driving generators or driven machines. In this case, the energy content of a fuel is used for producing a rotary movement of a turbine shaft. To this end, the fuel is burned in a combustion chamber, in the course of which air compressed by an air compressor is supplied. The working medium which is produced in the combustion chamber by the combustion of the fuel and is under high pressure and high temperature is directed in the process via a turbine unit, where it expands to perform work, arranged downstream of the combustion chamber.
In addition to the output which can be achieved, and in addition to a compact type of construction, an especially high efficiency is normally a design aim when designing such gas turbines. In this case, for thermodynamic reasons, an increase in the efficiency can in principle be achieved by an increase in the outlet temperature with which the working medium flows out of the combustion chamber and into the turbine unit. Temperatures of about 1200° C. up to 1300° C. are therefore aimed at and are also achieved for such gas turbines.
At such high temperatures of the working medium, however, the components exposed to said working medium are subjected to high thermal loads. In order to nonetheless ensure a comparatively long service life of the relevant components with high reliability, cooling of the relevant components, in particular of moving and guide blades of the turbine unit, is normally provided. Furthermore, provision can be made to cool the combustion chamber with cooling medium, in particular cooling air.
DE 195 44 927 A1 discloses a gas turbine which has an air compressor arranged upstream of a combustion chamber and opening into a diffuser. In the diffuser, a partial flow of the compressed air can be branched off from said diffuser and used for cooling structural parts, for example turbine blades of the gas turbine. However, the branching-off of the cooling air from the diffuser is only suitable for branching off a relatively small partial flow from the air flow leaving the air compressor. On the other hand, the main air flow directed through the diffuser is deflected in the direction of the combustion chamber and fed to the latter as combustion air. It is thus likely that components arranged downstream of the diffuser, i.e. relative to the direction of flow of the working medium flowing through the turbine, can only be cooled to a restricted extent.
Furthermore, DE 196 39 623 discloses a gas turbine which has a diffuser and in which the cooling air is bled by means of a tube projecting into the outlet of the diffuser. The compressed air used for combustion in an annular combustion chamber is in this case diverted in the direction of the burner by means of a C-shaped plate. Both during the bleeding of the cooling air and during the directing of the burner air, flow losses may occur, which it is necessary to avoid.